Figure 5.

The ICF compartment is essential for the stabilization of the ECF parameters and AVP secretion. The solid black line illustrates the prediction of the hydromineral parameters over a 24 h simulation when water exchange is permitted between the ECF and the ICF compartments (C, control condition). The solid gray line illustrates the same prediction when water exchange between the ECF and the ICF compartments is not permitted (C). In such a simulation, the ECF [Na⁺] quickly overpasses the threshold for drinking (A, dotted line 2). The additional need-induced water intake (four threshold crossing, A, dotted line 2) increases the total water intake by approximately 19% (F). Note that the absence of water exchange between the two compartments is characterized by larger fluctuations in the ECF [Na⁺] (A) and volume (D), as well as in AVP secretion (B).